Vacuum systems for manufacturing integrated circuits on wafers are generally known. A vacuum processing system may typically have a centralized vacuum chamber, called a transfer chamber, which may be part of a mainframe, for transferring wafers from one process chamber or load lock chamber to the next. A vacuum processing system may also typically have some kind of subsystem, such as a mini-environment, for providing the wafers to the load locks and other chambers and for collecting them back in order to send them on to the next system for processing. This transfer chamber plus the peripheral chambers and staging areas are sometimes called a cluster tool.
Between two vacuum chambers, such as the transfer chamber and one of the process chambers, is a slit valve. The slit valve includes an elongated rectangular opening for providing physical access between the two vacuum chambers. For example, when the slit valve is open, a robot in the transfer chamber may retrieve a wafer from one vacuum chamber and insert it into another vacuum chamber using a long, thin blade to hold the wafer.
After the wafer has been inserted into a vacuum chamber, the slit valve may be closed and sealed with a slit valve door by, for example, a pneumatic actuator. The slit valve door usually forms an airtight seal for the slit valve so that the pressure differential between the two chambers will not cause a gas leak through the slit valve. A metal insert may be placed within the slit valve opening in order to form a better airtight seat for the slit valve door.
Slit valve doors have typically been made of metal. The metal-to-metal contact between a slit valve door and the metal insert may provide a very good seal, but metal-to-metal contact may create microscopic particles that scrape off of the metal and get into the otherwise relatively clean environment of the vacuum chambers. Such particles may land on the wafers in the chambers, thereby contaminating them. Such contamination is undesirable in the processing of wafers.
To reduce the contamination by particles from the slit valve, an O-ring has typically been placed in a groove in the slit valve door. Thus, metal-to-metal contact is avoided, so no particles are thereby generated, and the O-ring can provide a satisfactory seal for the slit valve in many applications.
However, since the seal between the O-ring and the slit valve is not static, but rather is constantly being opened and closed such that there is rubbing and abrading on the O-ring from the slit valve insert, some particle generation, typically from the O-ring, still may occur.
U.S. Pat. No. 6,089,543 discloses a two piece slit valve door comprising a seal plate mounted on a mounting member. The seal plate, which actually contacts the slit valve, has a molded-in-place seal for making the contact and preventing metal-to-metal contact between the door and the valve. The seal may have a parabolic profile and may be adhesively bonded within a groove in the seal plate.
Another consideration when utilizing a resilient seal is controlling the size of the gap between the door and chamber to eliminate dynamic metal-to-metal scrubbing of the door and slit valve and/or overcompression of the seal. Controlling the size of this gap can also protect the seal from excessive exposure to the harsh chemicals that may exist in the chamber. Typically, controlling the gap size has involved tedious adjustment of the door and/or calibration of the actuator.
Traditional slit valve doors utilizing a resilient seal, such as a vulcanized fluorocarbon seal or a perfluorinated o-ring, typically have relied on the clean dry air (CDA) pressure setting of the slit valve pneumatic actuator to control the size of the gap between the door and valve and, thus, the seal compression. Fatiguing of the o-ring or vulcanized seal through dynamic cycling of the slit valve door can result in plastic deformation of the elastomer which leads to inconsistent gapping between the slit valve door and the slit valve (and/or insert). Inconsistent gapping can result in seal over-compression, metal-to-metal contact between the slit valve door and the slit valve, high exposure levels of the sealing element to corrosive process gases, and premature degradation of the seal.